Turbo machine

ABSTRACT

A turbomachine has a shaft extending along and rotatable about an axis and having an outer surface, a first impeller wheel permanently mounted on the shaft and having a respective back face, a second impeller wheel detachably mounted on the shaft axially offset from the first impeller wheel and having a respective back faces axially confront the back face of the first impeller wheel, and respective first and second axial bearings each having a respective rotor bearing half fixed to the respective impeller wheel and a respective nonrotatable stator bearing half axially juxtaposed with the respective rotor bearing half. The rotor shaft is of increasingly smaller cross-sectional size from the first wheel to the second wheel.

FIELD OF THE INVENTION

The present invention relates to a turbomachine. More particularly thisinvention concerns a turbomachine two axially spaced but jointlyrotatable impeller wheels.

BACKGROUND OF THE INVENTION

A turbomachine is known having at least one first and one secondimpeller wheel whose back faces confront each other, a rotor shaftcarrying both of the radial impeller wheels, and a bearing system.Adjacent each of the radial-blade impeller wheels is an axial bearingwith one respective rotor bearing half and one respective stator bearinghalf. The rotor bearing halves are each formed on the back face of therespective radial impeller wheel.

In practice, to contain the axial thrust of a rotor of a turbomachineusing a magnetic bearing system, axial bearing surfaces are customarilyused that are either formed directly on the shaft, or fixed by anadditional axial bearing washer to the shaft. Correspondingly,turbomachines having an axial magnetically mounted rotor shaft are knownin which the magnetic bearing halves for axial bearing are on an axialbearing washer, or on opposed shaft shoulders shrunk onto the rotorshaft.

EP 2 017 435 A2 describes a design having the features cited above for aturbomachine having as short a rotor as possible, and a rotor mass thatis as small as possible. Because the rotor bearing halves are formed onthe back faces of the radial impeller wheels, the space taken up by theaxial bearing can be reduced significantly, the axial bearing halvesbeing integrated into a housing wall and also integrated into the rearside of the radial impeller wheels, which must also be presentindependent of the bearing. The number of separate components is therebyreduced. The design known from EP 2 017 435 A2 is substantiallysymmetrical starting at an electric machine located centrally of therotor between the two radial impeller wheels. Starting at the electricmachine, sequentially in both directions, a radial magnetic bearing, asafety bearing, an opening through the assigned stator bearing halfhaving an interior shaft gasket and finally at the end of the rotorshaft, the corresponding impeller wheel is mounted overhung. Starting atthe electric machine, the diameter of the rotor shaft decreases in bothdirections successively, according to the cited components that areprovided along the rotor shaft. During assembly, first the rotor shaftmust be inserted through with the electric machine into the housing, thefurther components and finally the two impeller wheels are theninstalled on the two shaft ends. To make subsequent maintenancepossible, the turbomachine must be accessible on both sides, and bothaxial impeller wheels must be made removable as well.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved turbomachine.

Another object is the provision of such an improved turbomachine thatovercomes the above-given disadvantages, in particular that is simple toassemble and disassemble as well as to maintain.

SUMMARY OF THE INVENTION

A turbomachine has according to the invention a shaft extending alongand rotatable relative to a support about an axis and having an outersurface. A first impeller wheel permanently mounted on the shaft has arespective back face. The outer surface of the shaft is formed withsteps of increasingly small diameter away from the first wheel. A secondimpeller wheel detachably mounted on a respective one of the steps ofthe shaft axially offset from the first impeller wheel has a respectiveback face axially confronting the back face of the first impeller wheel.Respective first and second axial magnetic bearings each have arespective annular rotor bearing half fixed to the respective impellerwheel and a respective one-piece nonrotatable annular stator bearinghalf axially juxtaposed with the respective rotor bearing half, axiallyspacedly traversed by the shaft, and carried on the support. A radialbearing mounted on the rotor shaft between the axial bearings has aninner rotor ring carried on a respective one of the steps and an outerstator ring carried on the support.

According to the invention, an asymmetric design is provided, and thefirst impeller wheel is mounted fixedly and nonremovably on the rotorshaft. Thus according to the invention the first radial impeller wheelcannot be separated from the rotor shaft, or can be separated from therotor shaft only upon the exertion of a very large force or by takingspecial steps. Thus, it is possible, for example, to shrink the firstaxial impeller wheel onto the rotor shaft, to weld it or to press itonto the rotor shaft. Then, during assembly, starting with the firstradial impeller wheel that is connected nonremovably, the furthercomponents, i.e. at least the stator bearing halves and finally thesecond radial impeller wheel are installed sequentially. According tothe invention the individual steps of the shaft outer surface have outerdiameters adapted to the inner diameters of the respective components tobe mounted thereon. The individual components can easily be pushed up tothe section at which they are to be mounted. As a result of theremovable design of the second radial impeller wheel—depending on thedesign—disassembly or at least maintenance of the described componentsis possible. In particular, the components of the axial bearings areaccessible starting from the second radial impeller wheel.

Because the stator bearing halves are pushed onto the rotor shaft fromone end during assembly, separation into two half shells or segments isnot required, as a result of which stability and impermeability areimproved and production expense is also reduced.

To form an axial bearing, in particular an actively controllable axialbearing, magnetic windings of one of the halves of each bearing generatea magnetic field affecting the other bearing half, preferablycontrollable as needed. For practical reasons it is advantageous whenthe magnetic windings are in the fixed stator bearing halves.

To form a magnetic axial bearing, the rotor bearing halves must consistof a suitable material that magnetically interacts with the coils, or becovered with permanent magnets. Often, the material used for impellerwheels is not suited for forming rotor bearing halves of a magneticbearing. In such a case, at least one of the radial impeller wheels canbe formed by an impeller wheel body that includes a blade system and adisk consisting of a different material, e.g. an aluminum alloy,fastened at the rear side of the impeller wheel body, the disk formingthe rotor bearing half of the corresponding axial bearing. Such a diskor such a ring with a central opening for the rotor shaft can, forexample, be welded onto the impeller wheel body. To make precise weldingpossible, in particular, a connection by friction welding can beprovided. Alternatively, it is also possible to provide a suitablematerial, for example, permanent magnets or a magnetizable material inthe form of segments on the rear side of the radial impeller wheels, inparticular to insert them into corresponding recesses.

The assembly and the optionally provided disassembly from one endpermits, within the scope of the invention, that the first radialimpeller wheel with further machine components is also mounted fixedlyin a main housing. Advantageously, it is then provided that the rotorshaft extends out of the main housing, as a result of which the secondradial impeller wheel is correspondingly located outside the mainhousing.

The turbomachine having at least two radial impeller wheels whose backfaces confront each other (back-to-back arrangement), can serve as acompressor, expander or compander. While with a compressor having twocompressor impeller wheels a drive, in particular by an electricmachine, is to be provided, in the case of an expander having twoimpeller wheels, the energy that is being released can be recovered andused by an electric machine in the form of a generator. In the case of acompander having a compressor impeller wheel and an expander impellerwheel, an electric machine is only optionally provided, and it can beoperated as a generator or as a motor depending on application.

According to a preferred design of the invention, the two radialimpeller wheels are mounted overhung at respective ends of the rotorshaft. But in principle, it is also conceivable that on at least one ofthe two radial impeller wheels, the rotor shaft extends beyond thisradial impeller wheel, and still at least one further device can bemounted on the rotor shaft, for example, a further radial impellerwheel.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 shows components of a turbomachine according to the invention;and

FIG. 2 shows the system according to FIG. 1 attached to a main housing.

DETAILED DESCRIPTION

As seen in FIG. 1 a turbomachine according to the invention has a firstimpeller wheel 1 and a second impeller wheel 2 with respective backfaces 3 a and 3 b turned axially relative to an axis A toward each otherin a so-called back-to-back arrangement. The two wheels 1 and 2 arecarried by and rotationally fixed to a common axially centered rotorshaft 4 mounted on a bearing system that in turn is carried on a fixedsupport indicated schematically at 17 and constituted by a machinehousing.

The bearing system includes respective axial bearings 5 a and 5 b eachhaving a rotor bearing half 6 a or 6 b and a stator bearing half 7 a or7 b. The rotor bearing halves 6 a and 6 b are formed on back faces 3 aand 3 b of the respective assigned radial impeller wheels 1 and 2. Thestator halves 7 a and 7 b are carried on the fixed support 17.

According to the invention, the first radial impeller wheel 1 ispermanently mounted on to the rotor shaft 4, for example by shrinkingon, while the second radial impeller wheel 2 can be detached from theshaft 4. Thus, during assembly, the two stator bearing halves 7 a and 7b and then the second radial impeller wheel 2 can be pushed in sequenceonto the rotor shaft 4 to which the wheel 1 has already been fixed. Tomake this possible, the rotor shaft 4 decreases in cross-sectional sizeor diameter from the first radial impeller wheel 1 toward the secondimpeller wheel 2. Disassembly of the rotor system is also possible inreverse order.

FIG. 1 further shows that the stator bearing halves 7 a and 7 b eachhave a respective one-piece support 8 having an axially centered andthroughgoing hole for the rotor shaft 4 and an electromagnetic winding 9set in a groove formed in the respective support 8. In contrast, therotor halves 6 a and 6 b on the back faces 3 a and 3 b of the radialimpeller wheels 1 and 2 consist of a material that interactsmagnetically with the magnetic windings 9. Thus the rotor bearing halves6 a and 6 b are for example fitted with permanent magnets, magnetizablematerial or a material in which an opposing field is induced.

The specific embodiment according to FIG. 1 shows by way of example adesign in which the first radial impeller wheel 1 is comprised of a body10 formed with axially and radially extending blades and a flat disk 11of a different material integrally fixed to the rear side of the body10. The disk 11 forms the rotor bearing half 6 a of the correspondingaxial bearing 5 a and is of a material selected for its magneticproperties. The rotor half 6 a of the annular disk 11 with an axiallycentered and throughgoing through hole can, for example, be permanentlyconnected to the blade body 10 by friction welding.

FIG. 1 further shows that the axially oppositely effective bearings 5 aand 5 b flank a radial bearing 12 mounted on the rotor shaft 4 andformed as a magnetic bearing with an inner rotor ring 13 carried on theshaft 4 and an outer stator ring 14 carried on the fixed support 17.While the stator ring 14 has magnetic windings 18, the rotor ring 13consists of a material with suitable magnetic properties to form aradial magnetic bearing together with the magnetic windings 18 of thestator ring 14.

It can be seen that during assembly, first one stator bearing half 7 a,then the radial bearing 12, then the other stator bearing half 7 b, andfinally the second radial impeller wheel 2 with the corresponding rotorbearing half 6 b mounted on its back face 3 b, are installed, one afterthe other. To facilitate assembly, the diameter of the rotor shaft 4decreases in steps each intended to carry a respective one of thedescribed components.

Within the scope of the design according to the invention, the describedconfiguration is not only to be assembled successively, but can also inreverse sequence be at least partially disassembled, so that subsequentmaintenance or the exchange of individual components is still possible.

For example, the first impeller wheel 1 can be fixed with other machinecomponents in a main housing 15, with the rotor shaft 4 extending out ofthe main housing 15 and the second radial impeller wheel 2 mountedoutside the main housing 15. A corresponding design is shown in FIG. 2.The advantage results that during assembly, maintenance, and disassemblyof the bearing system, the main housing 15 can remain closed, while onlyan additional housing 16 that covers the bearing system must be removed.

In principle, the turbomachine can also have an electric machine 19 thatis provided together with the radial bearing 12 between the radialimpeller wheels 1 and 2. This machine 19 can be a motor, a generator, ora motor/generator.

Furthermore, the radial impeller wheels 1 and 2 can also be mountedoverhung, that is each at a respective end of the rotor shaft 4. But theinvention is not limited to this type of design. In principle, it isalso possible that the rotor shaft 4 extends beyond at least one of thetwo radial impeller wheels 1 and 2, for instance into the housing 15.

1. A turbomachine comprising: a support; a shaft extending along androtatable relative to the support about an axis and having an outersurface; a first impeller wheel permanently mounted on the shaft andhaving a respective back face, the outer surface of the shaft beingformed with steps of increasingly small diameter away from the firstwheel; a second impeller wheel detachably mounted on a respective one ofthe steps of the shaft axially offset from the first impeller wheel andhaving a respective back face axially confronting the back face of thefirst impeller wheel; respective first and second axial magneticbearings each having a respective annular rotor bearing half fixed tothe respective impeller wheel and a respective one-piece nonrotatableannular stator bearing half axially juxtaposed with the respective rotorbearing half, axially spacedly traversed by the shaft, and carried onthe support; a radial bearing mounted on the rotor shaft between theaxial bearings and having an inner rotor ring carried on a respectiveone of the steps and an outer stator ring carried on the support.
 2. Theturbomachine defined in claim 1, wherein the first radial impeller wheelis shrunk onto the rotor shaft.
 3. The turbomachine defined in claim 1,wherein the stator bearing halves each have a one-piece support havingan axially throughgoing hole through which the rotor shaft passes. 4.The turbomachine defined in claim 1, wherein at least one of the radialimpeller wheels is formed by an impeller wheel body including a bladesystem and a disk of a different material mounted on the rear side ofthe impeller wheel body, the disk forming the rotor bearing half of therespective axial bearing.
 5. The turbomachine defined in claim 1,wherein the first radial impeller wheel is fixedly mounted together withfurther machine components in a main housing, the rotor shaft extendingout of the main housing, the second radial impeller wheel being mountedoutside the main housing.
 6. The turbomachine defined in claim 1,wherein an electric machine is provided between the radial impellerwheels.
 7. The turbomachine defined in claim 1, wherein both radialimpeller wheels are mounted overhung at respective ends of the rotorshaft.